This invention relates to measuring devices, and more particularly to measuring devices having a digital read-out.
Attempts have been made to adapt digital read-out technology to conventional measuring devices. The prior art digital measuring devices usually use a self-contained light source, a light sensing means, optic fibers, and electronic apparati for translating the light energy into a digital read-out.
For example, U.S. Pat. No. 4,143,267, issued to Johnson et al., discloses a distance measuring device using a binary encoded scale on a movable tape measure, an optical detection system and an electronic circuit. The optical detection system, which decodes the binary information on the tape measure, basically comprises a self-contained light source, a plurality of light-conducting fibers and photo-transitor integrated circuits. The electronic circuit then accepts the digital code from the optical detection system, decodes it and displays the resulting information at a digital read-out.
Similarly, U.S. Pat. No. 4,161,781, issued to Hildebrandt et al., and U.S. Pat. No. 4,242,574, issued to Grant, each disclose coilable tape measures provided with a series of markings to indicate predetermined distances. Photo-electric sensor systems in the respective stationary tape housings detect shifts in light level at the illuminated markings when the tape measure is moved a particular distance. Each of these references use a battery to energize a self-contained light source.
Thus, the three above-discussed prior art devices teach the use of electronic apparati to produce light, to detect the light produced and/or to transform a light-detection signal into a digital read-out via optic fibers.
U.S. Pat. No. 3,857,361, issued to Gibson et al, also discloses the use of optic fibers with a digital read-out, but not in a distance or length measuring device. This patent discloses a UHF channel indicator for television tuners and the like to be used with a fairly conventional VHF channel indicator. Basically, this patent discloses a stationary optic fiber bundle (J), having near one end a first rotating plate (I) made up of two discs 24 and 26 each having opaque masks positioned annularly thereon, and a second rotatable plate (G) at the other end of the optic fiber bundle (J) and having both annularly positioned transparent numbers (for VHF), and a transparent window (F) to indicate UHF channel numbers formed at the ends of the bundle of fibers. The first plate is connected to the UHF dial (16) on the outside of the TV and the second plate is connected to the VHF dial (10) on the outside of the TV. Preferably, the optic fiber bundle (J) contains enough fibers to produce two separate digits adjacent the second plate (G), a tens digit and a units digit. In addition, a first light source (K) is located opposite the optic fiber bundle (J) on the far side of the first plate (I) and a second light source (H) is positioned near the second plate. In operation, a viewer first turns conventional dial (10) until the transparent window (F) is positioned adjacent the end of the optic fiber bundle (J). Then, a viewer turns UHF dial (16) on the television, and the first plate (I) is caused to turn. Various transparent areas on the first plate allow light to pass into various of the optic fibers. The optic fibers lighted show up through the transparent window (F) as channel digits at the digital read-out at the exterior of the television.
Although the prior art described above satisfies some of the objects to which optic fiber digital read-out devices are directed, the prior art still does not teach a digital measuring device which is trouble-free in operation, and is capable of the most cost-efficient production and the most covenient use.